Garage door openers are characteristically comprised of two primary components, namely a motor and a chain. The motor is mounted in a housing. The housing is suspended from the garage ceiling, set back from the garage door. Typically a long piece of metal channel extends from the housing to the garage wall above the door. The chain runs in or on the channel. The distal end of the channel is rigidly affixed to the wall above the garage door. Ordinarily the chain is a heavy gauge endless or circular chain. An arm extends from the chain to the top of the garage door. The chain turns around, and is driven by, a drive sprocket extending from the motor. The chain also turns around an idler sprocket or the like at the opposite end of the channel adjacent the wall above the garage door.
When engaged, the motor turns the drive sprocket. The drive sprocket turns the chain thereby causing the arm and, consequently, the garage door to move either toward or away from the motor. The motor is attached to the garage ceiling by means of two or more metal bars or struts, the upper ends of which are ordinarily rigidly mounted to the wood trusses above the ceiling.
As garage doors are heavy, the garage door opener motor must be sufficiently powerful in order for it to lift the door by pulling the arm along the channel. The supports attaching the motor housing to the ceiling must be sufficiently strong to bear the static weight of the motor as well as the additional strain created when the motor is running and the chain and garage door are in motion.
When operating, the running of the motor, and in particular, the action of the sprocket and chain, create significant vibration. This vibration is evidenced by significant noise in the garage and by the generation of acoustic frequency vibration transmitted to the structure of the building via the struts which are rigidly attached to the ceiling and thus through to the ceiling joists above. The vibration is also transmitted through the end of the channel where it is rigidly mounted to the wall above the garage door. The struts and chain channel, being both rigid, are good conduits of the acoustic frequency vibration. The vibration generated by the motor and chain operation is transmitted through the struts, and to a lesser degree through the chain channel, into the structure of the building resulting in noise being heard inside the building. Although Applicant does not wish to be bound by any particular theory of operation, it is postulated that the acoustic frequency vibration created by the motor and chain is transmitted into the structural framework of the building. Thus, being of a dense mass, the framework effectively transmits the acoustic frequency vibration to other parts of the building. In addition, the space between the walls of the building each covered, for example, by drywall, may act to amplify the sound. In the case in many multi-unit buildings where the framework of the building is concrete or steel, the structure makes an excellent transmitter of sound.
Hence, there is a need for, and it is one object of the present invention to provide a means to attenuate the structure-borne acoustic vibration created by the operation of a conventional garage door opener.